350 Scientific Intelligence. 



fifteen minutes to an hour. These do not seem explicable other- 

 wise than by correlated variations of gravity. These perturba- 

 tions often .exceed -£ w of a millimeter. They seem to be un- 

 doubted and the author is arranging an apparatus constructed 

 with great care for further observations. — Phil. Mag., March 

 1893; Comptes Pendus, January 30, 1893. J. T. 



6. Simple apparatus for the determination of the Mechanical 

 Equivalent of Heat. — C. Christiansen describes with figures a 

 simple apparatus for the determination of this important constant. 

 Two trials gave J=42900, J = 43080. The cost of the apparatus 

 is 175 marks. — Ann. der Physik und Chetnie, No. 2, 1893, pp. 

 374-376. j. t. 



7. On a certain Asymmetry in Concave Gratings. — Dr. J. 

 R. Rydberg discusses this subject and explains the asymmetry 

 observed. Since the two sides of the gratings often give spectra 

 of different brightness, the author believes that one can conclude 

 that the furrows which the point of the diamond makes in the 

 reflecting surface are not symmetrical in section. This explana- 

 tion is not insisted upon, but is merely given as a possible 

 explanation. The adjustments for getting rid of asymmetry are 

 given in detail. — Phil. Mag., March, 1893, pp. 190-199. j. t. 



8. Potential of Electric Charges. — Various investigations 

 differ widely in their measures of the charge on spheres raised to 

 different potentials. A. Heydneiler reviews the subject and 

 appends a table in C. G. S. units which gives the charge on 

 spherical electrodes of various radii, at variable distances apart 

 of these electrodes. — Ann. der Physik unci Chernie, No. 2, 1893, 

 pp. 213-235. j. T. 



9. Sensitive Galvanometer. — H. E. J. G. DuBois and H. 

 Rubens describe a new form of astatic galvanometer which they 

 believe excels other forms. Taking the nomenclature and classi- 

 fication recommended by Ayrton, Mather and Snmpner, (Phil. 

 Mag., xxx, p. 58, 1890), current sensitiveness S s is the deflec- 

 tion in scale divisions per micro-ampere, distance of scale being 

 2000 divisions and the full period of swing being 10 seconds. 



The ballistic sensitiveness S b is the deflection in scale divisions 

 per micro-coulomb, distance of scale being 2000 divisions. The 

 period of swing being 10 seconds with light suspensions. Ayrton's 

 table gives as the highest value S s r=413. The authors obtain a 

 value of S s =800. Tables of the ballistic sensitiveness are ap- 

 pended. — Ann. der Physik und Chemie, No. 2, 1893, pp. 236- 

 251. J. t. 



10. Experiments with Currents of High Frequency. — A. A. 

 Campbell Swinton states that he has succeeded in passing- 

 through his body sufficient electricity to bring the filament of au 

 ordinary 5 candle-power 100-volt incandescent lamp very nearly 

 to full incandescence or to bring the filament of a 32 candle-power 

 100-volt lamp to full redness. No sensation was experienced. The 

 apparatus consisted of an Apps coil, the primary of which was 

 supplied with a powerful make-and-break current. The secondary 



